A social-networking system, such as a social networking website, enables its users to interact with it and with each other through the system. The social-networking system may create and store a record, often referred to as a user profile, in connection with the user. The user profile may include a user's demographic information, communication channel information, and personal interest. The social-networking system may also create and store a record of a user's relationship with other users in the social-networking system (e.g., social graph), as well as provide services (e.g., wall-posts, photo-sharing, or instant messaging) to facilitate social interaction between users in the social-networking system. A geo-social-networking system is a social-networking system in which geographic services and capabilities are used to enable additional social interactions. User-submitted location data or geo-location techniques (e.g., mobile phone position logging) can allow a geo-social network system to connect and coordinate users with local people or events that match their interests. For example, users can check-in to a place using a mobile client application by providing a name of a place (or selecting a place from a pre-established list of places). The geo-social-networking system, among other things, can record information about the user's presence at the place and possibly provide this information to other users of the geo-social-networking system.
A geographic location of a mobile device (e.g., a cell phone, a tablet computer) equipped with cellular, Wi-Fi, or GPS (Global Positioning System) capabilities can be identified with geographic-positioning signals obtained by cell tower triangulation, Wi-Fi positioning, or GPS positioning. Such mobile devices may have additional functionalities incorporating geographic location data of the devices, for example, providing driving directions, displaying a map of a current location, or providing information of nearby points of interest such as restaurants, gas stations, etc.